Influence of Differential Diffusion on Super-Equilibrium Temperature in Turbulent Non-Premixed Hydrogen/Air Flames |
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Authors: | Olivier Gicque Dominique Thévenin Nasser Darabiha |
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Institution: | (1) Laboratoire EM2C, Ecole Centrale Paris, Chatenay Malabry, F92295, France;(2) Presently at LSS, University of Magdeburg “Otto von Guericke”, D-39106 Magdeburg, Germany |
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Abstract: | In this paper we wish to investigate the occurrence of super-equilibrium temperature values, observed in many experimental
configurations. We would like to understand the origin of this phenomenon. Previous authors have already shown that differential
diffusion can lead to considerable changes in the temperature field and we would like to build on top of this observation.
We investigate numerically super-equilibrium combustion by considering both laminar counter-flow and turbulent diluted hydrogen/air
diffusion flames. These turbulent flames are computed using direct numerical simulations (DNS). A detailed reaction mechanism
is employed and the transport properties are modeled using multicomponent diffusion velocities, including the Soret effect.
Analyzing these results we introduce three complementary parameters (dilution-free mixture fraction, dilution excess and local
enthalpy) to describe the local combustion conditions. Introducing a measure of dilution separately from the mixture fraction
is necessary for a proper analysis. Using this set of parameters it becomes possible to explain super-equilibrium temperature
levels as a consequence of differential diffusion. |
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Keywords: | DNS hydrogen super-equilibrium temperature differential diffusion |
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